Image forming apparatus

ABSTRACT

An image forming apparatus includes a light source, an optical deflector, an optical deflector casing, a bearing, and a sound absorption unit. The optical deflector reflects and deflects an optical beam emitted from the light source, having a rotational reflection member disposed on a rotation shaft to perform optical scanning. The optical deflector casing seals a space in which the optical deflector. The bearing rotatably supports the rotation shaft of the rotational reflection member with respect to the optical deflector casing, and includes at least portion exposed to an external space outside the sealed space of the optical deflector casing. The sound absorption unit is disposed opposite the exposed portion of the bearing with the external space therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.14/947,474, filed on Nov. 20, 2015, which is based on and claimspriority pursuant to 35 U.S.C. §119 to Japanese Patent Application No.2014-239787, filed on Nov. 27, 2014, in the Japan Patent Office, theentire disclosure of each of which is hereby incorporated by referenceherein.

BACKGROUND OF THE INVENTION

Technical Field

Exemplary aspects of the present invention relate to an image formingapparatus.

Description of the Related Art

Conventionally, image forming apparatuses including an optical deflectorand an optical deflector casing are known. The optical deflectordeflects an optical beam emitted from a light source to perform opticalscanning. The optical deflector casing provides a sealed space in whichthe optical deflector is disposed.

SUMMARY

In at least one embodiment of this disclosure, there is provided animproved image forming apparatus that includes a light source, anoptical deflector, an optical deflector casing, a bearing, and a soundabsorption unit. The optical deflector reflects and deflects an opticalbeam emitted from the light source, having a rotational reflectionmember disposed on a rotation shaft to perform optical scanning. Theoptical deflector casing seals a space in which the optical deflector.The bearing rotatably supports the rotation shaft of the rotationalreflection member with respect to the optical deflector casing, andincludes at least portion exposed to an external space outside thesealed space of the optical deflector casing. The sound absorption unitis disposed opposite the exposed portion of the bearing with theexternal space therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other aspects, features, and advantages of thepresent disclosure are better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a schematic sectional view of a laser writing device and abottom sound-absorption device arranged in a copier according to anexemplary embodiment of the present invention;

FIG. 2 is a schematic diagram of the copier according to the exemplaryembodiment of the present invention;

FIG. 3 is a schematic diagram of a photoconductor and the peripherythereof in the copier;

FIG. 4 is a perspective views of a state in which a front cover of thecopier is opened;

FIG. 5 is a perspective view of the copier when a left exterior cover isremoved from the state illustrated in FIG. 4;

FIG. 6 is a perspective view of an inner surface of a front casing plateto which a front inner cover is fixed for the copier in the stateillustrated in FIG. 5;

FIG. 7 is a diagram of an attachment position of a sound absorptiondevice in the front inner cover;

FIG. 8 is a schematic diagram of a sound absorption device with aHelmholtz resonator;

FIG. 9 is a perspective sectional view partially illustrating the laserwriting device and the bottom sound-absorption device according to theexemplary embodiment;

FIG. 10 is a schematic sectional view of the bottom sound-absorptiondevice and the laser writing device in a configuration including a soundguide member; and

FIG. 11 is a schematic sectional view of the bottom sound-absorptiondevice and the laser writing device in a configuration including alabyrinthine structure.

The accompanying drawings are intended to depict exemplary embodimentsof the present disclosure and should not be interpreted to limit thescope thereof. The accompanying drawings are not to be considered asdrawn to scale unless explicitly noted.

DETAILED DESCRIPTION OF THE INVENTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that have a similarfunction, operate in a similar manner, and achieve similar results.

Although the exemplary embodiments are described with technicallimitations with reference to the attached drawings, such description isnot intended to limit the scope of the invention and all of thecomponents or elements described in the exemplary embodiments of thisdisclosure are not necessarily indispensable to the present invention.

Referring now to the drawings, exemplary embodiments of the presentdisclosure are described below. In the drawings for explaining thefollowing exemplary embodiments, the same reference codes are allocatedto elements (members or components) having the same function or shapeand redundant descriptions thereof are omitted below.

Hereinafter, an electrophotographic copier (hereinafter called “a copier500”) serving as an image forming apparatus according to an exemplaryembodiment of the present invention is described. In the presentexemplary embodiment, a monochrome image forming apparatus is describedas an example of the copier 500. However, the present exemplaryembodiment can be applied to a known color image forming apparatus.

First, a configuration of the copier 500 according to the exemplaryembodiment of the present invention is described with reference to FIG.2. In FIG. 2, the copier 500 includes an image forming unit 100, ascanner 200, a recording sheet bank 300, and an automatic documentfeeder 400. The scanner 200 serving as an image reading device isattached on the image forming unit 100, and the image forming unit 100is placed on the recording sheet bank 300. The automatic document feeder400 is attached on the scanner 200. The automatic document feeder 400 isrotatable around a back side (a rear side in FIG. 2) as a fulcrum. InFIG. 2, the copier 500 is illustrated in two dimensional space that isindicated by arrows X and Z.

The image forming unit 100 includes a drum-shaped photoconductor 10,serving as a latent image bearer, that rotates in a direction indicatedby an arrow “A” shown in FIG. 2. FIG. 3 is an enlarged schematic diagramillustrating the photoconductor 10 and the periphery thereof. Asillustrated in FIG. 3, a discharge lamp 9, a charging device 11 with acharging roller, a developing device 12, a transfer unit 13, and acleaning device 14 with a photoconductor cleaning blade 8 are arrangedin the periphery of the photoconductor 10. The developing device 12 usespolymerization toner manufactured by a polymerization method as toner.The developing device 12 allows the polymerization toner to adhere to anelectrostatic latent image on the photoconductor 10 using a developingroller 121 serving as a developer bearing member to develop theelectrostatic latent image as a tone image.

The transfer unit 13 includes a transfer belt 17 that is looped around afirst belt extension roller 15 and a second belt extension roller 16serving as roller members. The transfer belt 17 is pressed against acircumferential surface of the photoconductor 10 in a transfer positionB in which the toner image on the photoconductor 10 is transferred to arecording sheet P serving as a recording medium.

A belt cleaning blade 18 is disposed in a transfer belt cleaning area C,and contacts the first belt extension roller 15 via the transfer belt17. The belt cleaning blade 18 removes foreign substances such asresidual toner remaining on the transfer belt 17 and paper powder afterthe recording sheet P is separated from the transfer belt 17.

The image forming unit 100 includes a toner supply device 20 disposed onthe left side of the charging device 11 and the cleaning device 14illustrated in FIG. 1. The toner supply device 20 supplies a new tonerto the developing device 12.

The image forming unit 100 includes a sheet conveyance device 60 forconveying a recording sheet P fed from a recording sheet cassette 61 ofthe recording sheet bank 300 to a discharged sheet stacking unit 39through the transfer position B. The sheet conveyance device 60 conveysthe recording sheet P along a supply path R1 or a manual supply path R2and a sheet conveyance path R. A registration roller pair 21 is disposedon an upstream side of the transfer position B in a sheet conveyancedirection on the sheet conveyance path R.

A heat fixing device 22 is disposed on a downstream side of the transferposition B in the sheet conveyance direction on the sheet conveyancepath R. In the heat fixing device 22, a heat roller 30 serving as aheating member and a pressure roller 32 serving as a pressing membergrasp the recording sheet P to fix a toner image with heat and pressureon the recording sheet P.

The image forming unit 100 also includes a discharge bifurcating claw34, a discharge roller 35, a first pressure roller 36, a second pressureroller 37, and an elastic roller 38 on a downstream side of the heatfixing device 22 in the sheet conveyance direction. In addition, theimage forming unit 100 includes the discharged sheet stacking unit 39 onwhich the recording sheet P with the toner image fixed by the heatfixing device 22 is stacked.

Moreover, the image forming unit 100 includes a switchback device 42 onthe right side as illustrated in FIG. 2. The switchback device 42conveys a recording sheet P along a reverse path R3 and a re-conveyancepath R4. The reverse path R3 is bifurcated from a position of thedischarge bifurcating claw 34 on the sheet conveyance path R. Theconveyance path R4 guides the recording sheet P having passed thereverse path R3 to a position of the registration roller pair 21 of thesheet conveyance path R again. The reverse path R3 includes a switchbackroller pair 43, whereas the re-conveyance path R4 includes a pluralityof sheet conveyance rollers pairs 66.

As illustrated in FIG. 2, the image forming unit 100 includes a laserwriting device 47 on the left side of the developing device 12. Thelaser writing device 47 includes an optical scanning system including alaser light source, an fθ lens, and a polygon scanner. The polygonscanner includes a polygon motor 49 and a rotational polygon mirror 48serving as a rotational reflection member for scan operation.

The scanner 200 includes a light source 53, a plurality of mirrors 54,an optical imaging lens 55, and an image sensor 56 such as acharge-coupled device (CCD) image sensor. A contact glass 57 is disposedon the top of the scanner 200. The automatic document feeder 400includes a document setting table and a document stacking table that isprovided at a document discharge position. The automatic document feeder400 includes a plurality of document conveyance rollers that convey adocument from the document setting table to the document stacking tablevia a reading position on the contact glass 57 of the scanner 200.

The recording sheet bank 300 includes a plurality of recording sheetcassettes 61 arranged one on another. The recording sheet cassette 61stores recording sheets P such as paper. For example, the paper is arecording material and an overhead projector (OHP) film. Each of therecording sheet cassettes 61 includes an access roller 62, a supplyroller 63, and a separation roller 64. The supply path R1 connected tothe sheet conveyance path R of the image forming unit 100 is formed onthe right side of the recording sheet cassette 61 illustrated in FIG. 2.The supply path R1 also includes a plurality of sheet conveyance rollerspairs 66 for conveying the recording sheet P.

The image forming unit 100 includes a manual feed unit 68 disposed onthe right side in FIG. 2. The manual feed unit 68 includes a manual feedtray 67 such that the manual feed tray 67 can be opened and closed. Inthe manual feed unit 68, the manual supply path R2 is formed to guidethe recording sheet P set on the manual feed tray 67 to the sheetconveyance path R. The manual feed unit 68 includes an access roller 62,a supply roller 63, and a separation roller 64 as similar to therecording sheet cassette 61.

Next, operation of the copier 500 is described. When the copier 500 isused to make a copy of a document, a user turns on a main switch andsets the document on the document setting table of the automaticdocument feeder 400. In a case where the user makes a copy of a bookdocument, the user opens the automatic document feeder 400 and sets thebook document directly on the contact glass 57 of the scanner 200. Theuser closes the automatic document feeder 400 to press down the bookdocument.

Subsequently, when the user presses a start button, the document set onthe automatic document feeder 400 is moved to the contact glass 57through a document conveyance path by a document conveyance roller.Then, the scanner 200 is driven to read content of the document, and theread document is discharged on the document stacking table. As for thedocument directly set on the contact glass 57, when the user presses thestart button, the scanner 200 is immediately driven to read content ofthe document. When the content of the document is read, the scanner 200irradiates a surface of the document on the contact glass 57 with lightfrom the light source 53 while moving the light source 53 along thecontact glass 57. Subsequently, the scanner 200 guides the reflectedlight from the surface of the document to the optical imaging lens 55with the plurality of mirrors 54 to insert the light into the imagesensor 56, so that the image sensor 56 reads the content of thedocument.

In the copier 500, the document is read. At the same time, thephotoconductor 10 is rotated by a photoconductor driving motor. First, asurface of the photoconductor 10 is uniformly charged, for example, withapproximately −1000 V by the charging device 11. Then, the chargedsurface of the photoconductor 10 is irradiated with a laser beam fromthe laser writing device 47 according to the content of the documentread by the scanner 200, thereby forming an electrostatic latent imageon the surface of the photoconductor 10. An area (a latent image area)irradiated with the laser beam has a surface potential of 0 V to −200 V,for example. Subsequently, the developing device 12 allows toner toadhere to the electrostatic latent image to develop it as a toner image.

In the copier 500, when the start button is pressed, the access roller62 feeds recording sheets P from a recording sheet cassette 61corresponding to selected paper size among the plurality of recordingsheet cassettes 61 of the recording sheet bank 300. The recording sheetsP fed by the access roller 62 are separated one by one by the supplyroller 63 and the separation roller 64, and one recording sheet P isguided to the supply path R1. The recording sheet P is guided to thesheet conveyance path R by the sheet conveyance rollers pairs 66. Whenthe recording sheet P conveyed to the sheet conveyance path R contactsthe registration roller pair 21, the conveyance of the recording sheet Pstops.

In a case where the manual feed unit 68 is used, the user opens themanual feed tray 67 and sets one or a plurality of recording sheets P onthe manual feed tray 67. If the plurality of recording sheets P is seton the manual feed tray 67, only one recording sheet P is conveyed tothe manual supply path R2 by the access roller 62, the supply roller 63,and the separation roller 64. The recording sheet P is then guided tothe sheet conveyance path R by the sheet conveyance rollers pairs 66.When the recording sheet P guided to the sheet conveyance path Rcontacts the registration roller pair 21, the conveyance of therecording sheet P stops. Accordingly, the recording sheet P stopped bythe registration roller pair 21 is fed to the transfer position B by theregistration roller pair 21, which start to rotate in sync with theconveyance of a leading end of the toner image on the photoconductor 10to the transfer position B.

The transfer unit 13 transfers the toner image on the photoconductor 10to the recording sheet P fed to the transfer position B, so that asurface of the recording sheet P bears the toner image. After the tonerimage is transferred from the surface of the photoconductor 10, thecleaning device 14 removes a residual toner from the surface of thephotoconductor 10. Moreover, the discharge lamp 9 removes a residualpotential from the surface of the photoconductor 10. The removal ofresidual potential enables a surface potential to be averaged to areference potential between OV and -150 V, and the copier 500 becomesready for next image formation, which is begun by the charging device11.

Meanwhile, the recording sheet P bearing the toner image transferred inthe transfer position B is conveyed to the heat fixing device 22 by thetransfer belt 17. The heat fixing device 22 applies heat and pressurewhile the recording sheet P is conveyed between the heat roller 30 andthe pressure roller 32, thereby fixing the toner image on the recordingsheet P. Subsequently, the discharge roller 35, the first pressureroller 36, the second pressure roller 37, and the elastic roller 38provide elasticity to the recording sheet P. Then, the recording sheet Pis discharged and stacked on the discharged sheet stacking unit 39.

In duplex printing, in which images are formed on two sides of arecording sheet P, the discharge bifurcating claw 34 is switched. Thisenables the recording sheet P to be conveyed to the reverse path R3 fromthe sheet conveyance path R after a toner image is transferred and fixedon one side of the recording sheet P. The recording sheet P conveyed tothe reverse path R3 is conveyed to a switchback position 44 by the sheetconveyance rollers pairs 66, and is switched back by the switchbackroller pair 43. Subsequently, the recording sheet P is conveyed to there-conveyance path R4, and again guided to the sheet conveyance path Rby the sheet conveyance rollers pairs 66. The other side of therecording sheet P having passed the re-conveyance path R4 undergoes thesimilar process, so that a toner image is transferred.

FIG. 4 is a perspective view of a state in which a front cover 101 ofthe copier 500 is opened. In the copier 500 illustrated in FIG. 4, theautomatic document feeder 400 and the optical system inside the scanner200 are removed. Since the front cover 101 serving as an exterior coveris opened, a front inner cover 102 serving as an interior cover isexposed. In FIG. 4, moreover, a toner bottle in the toner supply device20 is removed, and a bottle setting slot 20 a in the front inner cover102 is opened. The bottle setting slot 20 a serves as an area into whichthe toner bottle is inserted. Moreover, the copier 500 includes a sheetcassette exterior cover 61 a including a handle for pulling out therecording sheet cassette 61. The sheet cassette exterior cover 61 a isdisposed below the front cover 101. In FIG. 4, the copier 500 isillustrated in three-dimensional space that is indicated by arrows X, Yand Z. Similarly, in FIGS. 5 and 6, the copier 500 is illustrated inthree-dimensional space indicated by arrows X, Y and Z.

FIG. 5 is a perspective view of the copier 500 with a left casing plate520 exposed when a left exterior cover 103 is removed from the stateillustrated in FIG. 4. FIG. 6 is a perspective view of an inner surfaceof a front casing plate 510 of the copier 500 in the state illustratedin FIG. 5. The front casing plate 510 is disposed inside the front innercover 102, and the front inner cover 102 is fixed to the front casingplate 510.

As illustrated in FIG. 6, the copier 500 includes a frontsound-absorption device 610 employing a Helmholtz resonator. The frontsound-absorption device 610 is disposed opposite the laser writingdevice 47 inside the front side of the copier 500.

FIG. 7 is a diagram of an attachment position of the frontsound-absorption device 610 in the front inner cover 102. As illustratedin FIG. 7, the front inner cover 102 includes a front sound-absorptiondevice mount 160 on an inner surface thereof. The front sound-absorptiondevice 610 is attached and fixed to the front sound-absorption devicemount 160 as indicated by an arrow illustrated in FIG. 7, and the frontinner cover 102 is fixed to the front casing plate 510. Accordingly, asillustrated in FIG. 6, the front sound-absorption device 610 projectsinward from a sound absorption device opening 510 a formed on the frontcasing plate 510.

Moreover, as illustrated in FIG. 2, the copier 500 includes a bottomsound-absorption device 620, serving as a sound absorption unit, belowthe laser writing device 47.

Each of the front sound-absorption device 610 and the bottomsound-absorption device 620 of the copier 500 according to the presentexemplary embodiment serves as a sound absorption device with aHelmholtz resonator.

FIG. 8 is a schematic view of a sound absorption device 600 with aHelmholtz resonator. The sound absorption device 600 is illustrated asan example of either the front sound-absorption device 610 or the bottomsound-absorption device 620. As illustrated in FIG. 8, the soundabsorption device 600 has a container-like shape with a narrow inlet,and includes a cavity portion 601 cavity and a communication portion603. The cavity portion 601 has a certain volume, and the communicationportion 603 is smaller than the cavity portion 601. The sound absorptiondevice 600 absorbs sound having a specific frequency, the sound comingto the communication portion 603. A frequency of sound that is absorbedby the sound absorption device 600 can be expressed as follows.

$\begin{matrix}{f = {\frac{c}{2\pi}\sqrt{\frac{S}{V( {H + {\Delta \; r}} )}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where “V” is a volume of the cavity portion 601, “S” is an area of anopening 602 in the communication portion 603, “H” is a length of thecommunication portion 603, “c” is a sound speed, and “f” is a soundabsorption frequency in the sound absorption device 600.

In Equation 1, “Δr” represents an opening edge correction. Generally,“Δr=0.6 r” is used where “r” is a radius when a cross section of thecommunication portion 603 is circle. As expressed by Equation 1, afrequency of sound absorbed by the sound absorption device 600 can bedetermined using the volume V of the cavity portion 601, the length H ofthe communication portion 603, and the opening area S of thecommunication portion 603.

The copier 500 generates various sounds such as a driving sound of adriving motor for transmitting rotation drive to various rollers, amoving sound of moving members such as various rollers, and a rotationsound of the polygon mirror 48 of the laser writing device 47. Suchsounds may be transmitted outside the copier 500 and is perceivable asnoise. The sound absorption device 600 is formed to deal with afrequency of a sound that needs to be prevented from being transmittedoutside.

FIG. 1 is a sectional view schematically illustrating the laser writingdevice 47 and the bottom sound-absorption device 620 of the copier 500according to the present exemplary embodiment. FIG. 9 is a perspectivesectional view partially illustrating the laser writing device 47 andthe bottom sound-absorption device 620 of the copier 500. FIG. 1 is theschematic sectional view of the laser writing device 47 and the bottomsound-absorption device 620 as seen from the left side of FIG. 9.

The laser writing device 47 includes a polygon scanner 4 serving as anoptical deflector. The polygon scanner 4 allows the polygon mirror 48serving as a rotational reflection member to reflect and deflect anoptical beam emitted from a light source, thereby performing opticalscanning. Moreover, the laser writing device 47 includes a casing 2serving as an optical deflector casing, and a bearing 3. The casing 2provides a polygon arrangement space 45, serving as a sealed space, inwhich the polygon scanner 4 is disposed. The bearing 3 rotatablysupports the polygon scanner 4 with respect to the casing 2. Asillustrated in FIG. 9, the casing 2 includes a casing cover 24 placed ona casing body 25 to form the polygon arrangement space 45. In thepresent exemplary embodiment, the polygon arrangement space 45 is asealed space in a strict sense, that is, movements of gas from and to anexternal unit are completely blocked. However, the polygon arrangementspace 45 is not limited thereto as long as movements of gas betweeninside and outside the polygon arrangement space 45 are blocked suchthat a foreign substance such as paper powder and dust outside does notget into the polygon arrangement space 45.

The polygon scanner 4 includes a polygon board 46 to which the polygonmotor 49 is fixed. The polygon board 46 is fixed to a polygon fixationunit 28 with a polygon fixation screw 46 a, so that polygon scanner 4 isfixed to the casing 2. The polygon fixation unit 28 is disposed on abottom wall 25 b of the casing body 25. In the polygon scanner 4, thepolygon mirror 48 is fixed to a shaft 40 that is a rotor of the polygonmotor 49. When the polygon motor 49 operates, the shaft 40 serving as arotation shaft and the polygon mirror 48 are rotated.

As illustrated in FIG. 1, the bearing 3 rotatably supports the shaft 40via a bearing member 41. In the present exemplary embodiment, an airbearing is used as the bearing member 41. However, the bearing is notlimited thereto, and a bearing different from the air bearing may beused as the bearing member 41. Moreover, in the casing 2 as illustratedin FIG. 1, a hole is provided on the bottom wall 25 b serving as abearing support wall for supporting the bearing 3, and the bearing 3 isfitted into the hole. Thus, one portion of the bearing 3 is exposed toan air cooling space 50, serving as an external space, from the casing2. The air cooling space 50 is provided outside the polygon arrangementspace 45, and serves as space where gas can be moved in and out. Thisenables the bearing 3 to be cooled by contact with outside air. In thepresent exemplary embodiment, the bearing 3 is a component attached tothe polygon motor 49, and outer circumference of the bearing 3 isattached to the hole provided on the bottom wall 25 b of the casing 2.

When the polygon motor 49 operates, heat is generated in the bearing 3by rolling resistance that is generated by rotation of the shaft 40 athigh speed. Thus, each member of the bearing 3 is heated. The aircooling space 50 allows the outside air to pass therethrough, and oneportion of the bearing 3 is exposed to the air cooling space 50.Accordingly, the bearing 3 is cooled by contacting the outside air, anda temperature rise due to rotation of the shaft 40 is suppressed. Suchcooling of the bearing 3 can in turn suppress the temperature rise nearthe polygon scanner 4.

If the bearing 3 of the polygon scanner 4 and the polygon mirror 48 wereto be disposed inside a sealed space, heat generated in the bearing 3would not escape. In such a case, a temperature of the air inside thesealed space rises. Such an air temperature rise inside the sealed spacecan cause deformation of parts of the optical system, such as a polygonscanner. The deformation of the member may change a beam path, and adesired image may not be obtained. In the copier 500 according to thepresent exemplary embodiment, on the other hand, the bearing 3 isexposed to the air cooling space 50 outside the polygon arrangementspace 45 serving as the sealed space in which the polygon mirror 48 isdisposed. Such arrangement can suppress a temperature rise of the sealedspace due to the heat generated in the bearing 3.

If the communication portion 603 of the Helmholtz resonator were to bedisposed toward the sealed space in which temperature tends to rise moreeasily with heat generated in the bearing 3, the following problem mightoccur. That is, if temperature of the air in the sealed space in whichthe communication portion 603 is disposed were to rise, sound speedwould accelerate. In such a case, an increase in value of the soundspeed “c” in Equation 1 changes a value of the sound absorptionfrequency “f” which is absorbed by the Helmholtz resonator. Such achange in the sound absorption frequency “f” causes the absorptionfrequency to shift with respect to a frequency of the sound generatedwhen the polygon scanner 4 is driven. Consequently, a desired soundabsorption effect cannot be obtained, or the sound generated when thepolygon scanner 4 is driven cannot be suppressed.

In the copier 500 according to the present exemplary embodiment, on theother hand, the communication portion 603 of the Helmholtz resonator isdisposed in the air cooling space 50 in which the outside air passes andtemperature does not tend to rise with heat generated in the bearing 3.This suppresses a shift in the sound absorption frequency of theHelmholtz resonator caused by the temperature rise of space in whichsound is absorbed, thereby maintaining a desired sound absorptioneffect.

As illustrated in FIG. 1, the bottom sound-absorption device 620 forabsorbing sound generated by rotation of the polygon mirror 48 isdisposed opposite the exposed bearing 3 with the air cooling space 50therebetween. This can suppress noise generated when the polygon scanner4 is rotated. In the polygon scanner 4, wind noise is generated byrotation of the polygon mirror 48. Moreover, in the bearing 3, the airbearing vibrates when the polygon mirror 48 rotates. The vibration ofthe air bearing causes pressure loss. A change in the pressure due tothe pressure loss generates sound. Although the bearing 3 not coveredwith the casing 2 is a source of the sound, the bottom sound-absorptiondevice 620 disposed directly below the bearing 3 can absorb the soundfrom the bearing 3 to suppress noise.

The casing 2 of the laser writing device 47 is fixed to a supportingmetal plate 540 with a casing screw 26. The supporting metal plate 540is fixed to the front casing plate 510 and a back casing plate 530 withsupporting plate fixation screws 541. The supporting metal plate 540includes a wall portion that extends in a vertical direction. The laserwriting device 47 is attached to the supporting metal plate 540 suchthat the wall portion is inserted into a position “α” shown in FIG. 9.The casing body 25 of the casing 2 includes a casing leg 25 a thatextends to a lower portion relative to the bottom wall 25 b. The casingleg 25 a is fixed to the wall portion of the supporting metal plate 540with a casing screw 26 to fix the casing 2 to the supporting metal plate540. Moreover, the supporting metal plate 540 includes an opening wherethe polygon scanner 4 is positioned. As illustrated in FIG. 1, thebottom wall 25 b of the casing 2 projects below the supporting metalplate 540.

A bottom casing plate 5 for the image forming unit is disposed below thesupporting metal plate 540. The bottom casing plate 5 is made of metal,and fixed to the front casing plate 510 and the back casing plate 530with bottom casing plate fixation screws 51. In the copier 500 accordingto the present exemplary embodiment, a burring process unit 5 a isdisposed in a position perpendicularly below the bottom casing plate 5serving as a structure member disposed below the polygon scanner 4, sothat the communication portion 603 is formed. The communication portion603 serves as a short pipe of the Helmholtz resonator. Moreover, a soundabsorption cover 6 closely contacts an undersurface of the bottom casingplate 5 with the burring process unit 5 a disposed. Accordingly, thebottom sound-absorption device 620 with the Helmholtz resonator isformed. The sound absorption cover 6 is fixed to the bottom casing plate5 with cover fixation screws 65.

The rotation of the polygon mirror 48 causes vibration in the bearing 3,and such vibration generates sound. The Helmholtz resonator with a soundabsorption frequency that is set to absorb such sound may receivesolid-borne vibration having substantially the same frequency as thesound absorption frequency. In such a case, the sound having such afrequency comes from the Helmholtz resonator. According to the copier500 in the present exemplary embodiment, the supporting metal plate 540and the bottom casing plate 5 are different members. The supportingmetal plate 540 supports the casing 2 into which the bearing 3 isfitted, and the bottom casing plate 5 forms the bottom sound-absorptiondevice 620 including the Helmholtz resonator. A path for enabling thevibration to be transmitted in a solid-borne manner from the bearing 3to the bottom casing plate 5 is provided by a plurality of differentmembers fixed by a fixation member. Herein, the configuration in whichthe different members are fixed by the fixation member represents aconfiguration in which the different members are separated when thefixation member such as a screw is released, instead of integration ofthe different members by welding.

In a case where one of the different members vibrates in a fixationportion in the configuration in which the different members are fixed bythe fixation member, relative displacement occurs with respect to theother member. In such a case, not all vibration energy is transmitted tothe other member, and the vibration energy is reduced. The fixationportion in which the different members are fixed by the fixation memberis arranged in the path for enabling the vibration to be transmitted ina solid-borne manner from the bearing 3 to the bottom casing plate 5.Such arrangement of the fixation portion in the path attenuates thevibration generated in the bearing 3, thereby suppressing transmissionof the vibration to the bottom casing plate 5. Accordingly, this cansuppress noise to be generated from the Helmholtz resonator of thebottom sound-absorption device 620 due to solid-borne vibration havingsubstantially the same frequency as a sound absorption frequency.

In the copier 500, the vibration generated in the bearing 3 istransmitted to the casing 2 and then to the supporting metal plate 540via the fixation portion provided with the casing screw 26.Subsequently, the vibration is transmitted to the front casing plate 510and the back casing plate 530 via the fixation portions provided withthe respective supporting plate fixation screws 541. The vibrationtransmitted to the front casing plate 510 and the back casing plate 530is transmitted to the bottom casing plate 5 via the fixation portionsprovided by the respective bottom casing plate fixation screws 51.Accordingly, there is a plurality of fixation portions in thetransmission path through which the vibration is transmitted in thesolid-borne manner from the bearing 3 to the bottom casing plate 5. Thisattenuates vibration energy each time the vibration is transmittedthrough the fixation portion. Therefore, such arrangement can suppresstransmission of the vibration generated in the bearing 3 to the bottomcasing plate 5 serving as a member for forming the Helmholtz resonator.

When the vibration is transmitted, the sound absorption cover 6generates sound louder than that generated by the bottom casing plate 5forming the Helmholtz resonator of the bottom sound-absorption device620. In the copier 500, since the vibration transmitted to the bottomcasing plate 5 is transmitted to the sound absorption cover 6 via thefixation portion provided with the cover fixation screw 65, thevibration at the sound absorption cover 6 is more attenuated than thatat the bottom casing plate 5. This can suppress generation of sound dueto transmission of the vibration to the sound absorption cover 6.

As illustrated in FIGS. 1 and 9, a lower end of the polygon fixationunit 28 disposed on the bottom wall 25 b extends toward the bottomcasing plate 5 according to a length of the polygon fixation screw 46 a.However, the lower end of the polygon fixation unit 28 does not contactthe bottom casing plate 5. In a case where the polygon fixation unit 28contacts the bottom casing plate 5, there is a possibility thatvibration of the casing 2 may be transmitted in the solid-borne mannerto the bottom casing plate 5 via the contact portion. The non-contactarrangement can prevent transmission of barely attenuated vibration tothe bottom casing plate 5.

Moreover, in the path for enabling vibration to be transmitted in thesolid-borne manner from the bearing 3 to the bottom casing plate 5, thevibration is transmitted via the front casing plate 510 or the backcasing plate 530. Each of the front casing plate 510 and the back casingplate 530 is a casing member serving as a frame of the copier 500, andis larger than other metal members of the copier 500. When vibration istransmitted from a member of a vibration source to a certain member viaa fixation portion, the vibration is spread over the certain member.Then, the vibration is further transmitted to a next member via anotherfixation portion different that of the vibration source. Herein, as thecertain member becomes larger, the amount of vibration energy consumedfor vibration of the entire certain member increases, and the vibrationto be transmitted to the next member can be attenuated. According to thecopier 500, in the path enabling the vibration to be transmitted in thesolid-borne manner, the vibration can be transmitted via the frontcasing plate 510 or the back casing plate 530. Thus, the vibrationtransmitted to the bottom casing plate 5 can be more attenuated thanthat transmitted via only other small members.

In the copier 500, the communication portion 603 serving as a short pipeof the Helmholtz resonator is formed in the bottom casing plate 5including a metal plate that provides a good sound insulation effect.Since the bottom casing plate 5 serves as a structure member forming aframe of the copier 500, the short pipe of the Helmholtz resonator canbe formed without an additional component. Moreover, the soundabsorption cover 6 forming the cavity portion 601 is made of resin, sothat the cavity portion 601 can be readily provided.

As illustrated in FIG. 1, the bottom sound-absorption device 620includes the short pipe inserted into the cavity portion 601, the shortpipe being formed by burring process. Thus, an edge of the burringprocessed metal plate is hidden to enhance safety. This can prevent anoperator from being disturbed by the burring processed portion when theoperator performs a mounting operation and a maintenance operation.

The bottom sound-absorption device 620 employs two members of the bottomcasing plate 5 and the sound absorption cover 6 to form the Helmholtzresonator. The sound absorption cover 6 is prepared in a shape such thatone side of space to be the cavity portion 601 is opened. This open sideis blocked by the bottom casing plate 5 to form the cavity portion 601.Thus, the cavity portion 601 with a predetermined volume can be readilyformed compared to formation of the cavity portion 601 with one member.

Moreover, since the bottom casing plate 5 is made of metal having ahigher density than resin of which the sound absorption cover 6 made,transmission of sound can be suppressed compared to a configuration inwhich the bottom casing plate 5 is made of only resin. Moreover, sincethe sound absorption cover 6 is made of resin with processing that iseasier than that of the bottom casing plate 5, a volume of the cavityportion 601 can be obtained with high accuracy while a sealed propertyremains compared to a configuration in which the sound absorption cover6 is made of only metal substantially the same as that of the bottomcasing plate 5. Accordingly, the volume of the cavity portion 601 isobtained, so that sound of a low frequency can be absorbed. Moreover,the cavity portion 601 is formed with high accuracy while a sealedproperty remains. This enhances a sound absorption effect.

In the bottom sound-absorption device 620, the bottom casing plate 5 andthe sound absorption cover 6 are fastened with the cover fixation screws65 as described above. Since the bottom casing plate 5 and the soundabsorption cover 6 are firmly tightened to enhance the degree ofsealing, a sound absorption effect can be enhanced in the bottomsound-absorption device 620 as the Helmholtz resonator.

FIG. 10 is a schematic sectional view of a sound guide member 201,serving as a wall-like projected unit, disposed on the bottom wall 25 bof the casing 2 of the laser writing device 47. The sound guide member201 surrounds the periphery of the bearing 3 such that sound generatedin the bearing 3 is guided toward the bottom sound-absorption device 620without leakage of the sound to the outside. The arrangement of thesound guide member 201 can suppress leakage of the sound from the aircooling space 50 near the bearing 3 to the outside while allowing air toflow to the air cooling space 50 near the bearing 3.

FIG. 11 is a schematic sectional view of a configuration with alabyrinthine structure 75 that is formed in the air cooling space 50between the laser writing device 47 and the bottom sound-absorptiondevice 620. The labyrinthine structure 75 is formed to surround theperiphery of the bearing 3. In the configuration illustrated in FIG. 11,double upper walls 202 serving as wall-like projected units are arrangedon the bottom wall 25 b of the laser writing device 47 illustrated inFIG. 1 such that the double upper walls 202 surround the periphery ofthe bearing 3. Moreover, a lower wall 69 serving as a wall-likeprojected unit is disposed such that one portion of the sound absorptioncover 6 projects not only between the double upper walls 202 but alsoupward from the bottom casing plate 5.

As illustrated in FIG. 11, the upper walls 202 and the lower wall 69 areoffset to form the labyrinthine structure 75 with a certain clearancethat allows air to move therethrough, thereby preventing heat fromremaining trapped inside the air cooling space 50 near the bearing 3.Hence, a temperature rise can be suppressed. Moreover, since thelabyrinth 75 structure has a complicated shape with a plurality of bentportions, a sound path is bent for a plurality of times for sound thatis to be transmitted from the air cooling space 50 near the bearing 3 tothe outside. When the sound is diffracted for a plurality of times, thesound becomes quieter. Accordingly, leakage of the sound from theclearance can be suppressed in spite of the presence of the clearance.The arrangement of the labyrinthine structure 75 enables the bottomsound-absorption device 620 to absorb the sound, and suppresses leakageof the sound from the air cooling space 50 near the bearing 3 to theoutside while allowing air to flow to the air cooling space 50 near thebearing 3.

The copier 500 serving as one example of an image forming apparatus canprovide effects described below.

[Aspect A]

An image forming apparatus such as the copier 500 includes an opticaldeflector such as the polygon scanner 4, an optical deflector casingsuch as the casing 2, a bearing such as the bearing 3, and a soundabsorption unit such as the bottom sound-absorption device 620. Theoptical deflector allows a rotational reflection member such as thepolygon mirror 48 to reflect and deflect an optical beam emitted from alight source to perform optical scanning. The optical deflector casingprovides a sealed space, such as the polygon arrangement space 45, inwhich the optical deflector is disposed. The bearing rotatably supportsa rotation shaft, such as the shaft 40, of the rotational reflectionmember with respect to the optical deflector casing. The soundabsorption unit with a Helmholtz resonator absorbs sound generated byrotation of the rotational reflection member. At least one portion ofthe bearing is exposed to external space, such as the air cooling space50, outside the sealed space from the optical deflector casing, and thesound absorption unit is arranged in a position opposite the exposedbearing with the external space therebetween. Accordingly, as describedabove in the exemplary embodiment, although heat is generated in thebearing by rotation of the rotational reflection member, such heat iscooled by gas of the external space. This can suppress a temperaturerise near the optical deflector when the optical deflector is driven.Moreover, although sound is generated in the bearing by rotation of therotational reflection member, such sound is absorbed by the soundabsorption unit arranged in the position opposite the bearing with theexternal space therebetween. This can suppress generation of sound whenthe optical deflector is rotationally driven. According to the aspect A,therefore, when the optical deflector is rotationally driven, generationof sound can be suppressed. Meanwhile, a temperature rise near theoptical deflector can be suppressed.

[Aspect B]

In the aspect A, a member, such as the bottom casing plate 5, that formsthe sound absorption unit and the optical deflector casing such as thecasing 2 are different members. Such a member and the optical deflectorcasing are connected via a fixation portion of at least one of othermembers such as the front casing plate 510 and the back casing plate530. Therefore, as described above in the exemplary embodiment, thevibration transmitted from the optical deflector such as the polygonscanner 4 to the optical deflector casing is attenuated when thevibration is transmitted in a solid-borne manner to another member viathe fixation portion. The vibration is further attenuated when beingtransmitted in the solid-borne manner from the other member to a memberof the sound absorption unit via the fixation portion. This can suppresstransmission of the vibration generated by rotation of the opticaldeflector to the member of the sound absorption unit, therebysuppressing generation of sound from the Helmholtz resonator of thesound absorption unit.

[Aspect C]

According to any of the aspects A and B, the member such as the bottomcasing plate 5 forming a wall arranged opposite the external space suchas the air cooling space 50 with respect to the sound absorption unitsuch as the bottom sound-absorption device 620 is made of metal.Therefore, as described in the exemplary embodiment, the wall of thesound absorption unit is made of metal that has a higher density thanresin and provides good sound insulation, so that transmission of soundcan be suppressed.

[Aspect D]

According to any of the aspects A through C, a communication unit suchas the communication portion 603 of the Helmholtz resonator in the soundabsorption unit such as the bottom sound-absorption device 620 is formedby drawing such as burring process. Accordingly, as described above inthe exemplary embodiment, a communication unit including an openingportion such as the opening 602 can be formed without arranging a newmember to form the communication unit with respect to a member thatforms one portion of a wall of a cavity such as the cavity portion 601,thereby reducing costs of the sound absorption unit such as the bottomsound-absorption device 620.

[Aspect E]

According to any of the aspects A through D, a short pipe forming thecommunication unit such as the communication portion 603 of theHelmholtz resonator in the sound absorption unit such as the bottomsound-absorption device 620 is entered into the cavity such as thecavity portion 601. Therefore, as described in the exemplary embodiment,an edge of the short pipe is hidden, and thus an operator is notdisturbed when performing operation such as mounting operation andmaintenance operation.

[Aspect F]

According to any of the aspects A through E, a member such as the soundabsorption cover 6 forming the cavity such as the cavity portion 601 ofthe Helmholtz resonator in the sound absorption unit such as the bottomsound-absorption device 620 is made of a moldable material such asresin. Accordingly, as described in the exemplary embodiment, the memberis made of a material that can be readily processed, and a volume of thecavity can be obtained with high accuracy while a sealed propertyremains. Thus, the volume of the cavity is obtained, so that sound of alow frequency can be absorbed. Moreover, the cavity is formed with highaccuracy while a sealed property remains. This enhances a soundabsorption effect.

[Aspect G]

According to any of the aspects A through F, there is a plurality ofmembers, such as the bottom casing plate 5 and the sound absorptioncover 6, that form the Helmholtz resonator of the sound absorption unitsuch as the bottom sound-absorption device 620. Accordingly, asdescribed above in the exemplary embodiment, the cavity such as thecavity portion 601 with a predetermined volume can be readily formedcompared to a case where the Helmholtz resonator of the sound absorptionunit is formed by only one member.

[Aspect H]

According to the aspect G, the plurality of members such as the bottomcasing plate 5 and the sound absorption cover 6 forming the Helmholtzresonator are fastened with screws such as the cover fixation screws 65.Therefore, as described in the exemplary embodiment, the plurality ofmembers are firmly tightened to enhance the degree of sealing, and ansound absorption effect can be enhanced in the sound absorption unitsuch as the bottom sound-absorption device 620 as the Helmholtzresonator.

[Aspect I]

According to any of the aspects A through H, a wall-like projected unit,such as the sound guide member 201, that surrounds the periphery of thebearing such as the bearing 3 is arranged on a surface opposite theexternal space such as the air cooling space 50 with respect to theoptical deflector such as the casing 2. Accordingly, as described abovein the exemplary embodiment, leakage of sound from the external spacenear the bearing to the outside can be suppressed while air is flowingto the external space near the bearing.

[Aspect J]

According to any of the aspects A through I, wall-like projected unitssuch as the lower wall 69 and the upper wall 202 surrounding theperiphery of the bearing such as the bearing 3 are arranged onrespective surfaces opposite the external space such as the air coolingspace 50 with respect to the sound absorption unit such as the bottomsound-absorption device 620 and the optical deflector casing such as thecasing 2. Moreover, a path extending from the inside of space surroundedby the projected units toward the outside via clearance formed by theprojected units has a shape that includes a plurality of bent portionssuch as the labyrinthine structure 75. With such a configuration, asdescribed above in the exemplary embodiment, leakage of sound from theexternal space near the bearing can be suppressed while air is flowingto the external space near the bearing, and the sound can be absorbed bythe sound absorption unit.

The present invention has been described above with reference tospecific exemplary embodiments. Note that the present invention is notlimited to the details of the embodiments described above, and variousmodifications and enhancements are possible without departing from thespirit and scope of the invention. It is therefore to be understood thatthe present invention may be practiced otherwise than as specificallydescribed herein. For example, elements and/or features of differentillustrative exemplary embodiments may be combined with each otherand/or substituted for each other within the scope of the presentinvention.

What is claimed is:
 1. An image forming apparatus comprising: a lightsource; an optical deflector having a rotational reflection memberconfigured to reflect and deflect an optical beam emitted from the lightsource, the optical deflector configured to perform optical scanning; anoptical deflector casing configured to seal a space in which the opticaldeflector is disposed; a bearing configured to rotatably support arotation shaft of the rotational reflection member on the opticaldeflector casing; and at least one sound absorption unit having anopening and a cavity portion, the at least one sound absorption unitdisposed opposite the bearing, with the opening located at a distancefrom an end of the bearing.
 2. The image forming apparatus according toclaim 1, wherein a diameter of the opening is smaller than a diameter ofthe bearing.
 3. The image forming apparatus according to claim 1,wherein the at least one sound absorption unit and the optical deflectorcasing are connected via at least one fixation portion.
 4. The imageforming apparatus according to claim 1, wherein the at least one soundabsorption unit includes: a metal portion configured to form theopening; and a resin portion configured to form the cavity portion. 5.The image forming apparatus according to claim 4, wherein the metalportion configured to form the opening is configured to be screwed tothe resin portion to form the cavity portion.
 6. The image formingapparatus according to claim 1, wherein the at least one soundabsorption unit includes a short pipe configured to form the opening,and wherein the short pipe is configured to be inserted into the cavityportion.
 7. The image forming apparatus according to claim 1, whereinthe at least one sound absorption unit includes a plurality of soundabsorption units.